CCSDS File Delivery Protocol (CFDP)âPart 1: Introduction and ...

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CCSDS REPORT CONCERNING THE CCSDS FILE DELIVERY PROTOCOL (CFDP) Sender Receiver M FD(1) FD(2) X FD(3) FD(4) FD(5) X NAK(FD(1)) FD(last) EOF ACK(EOF) NAK(FD(1)) FD(1) timeout X NAK(FD(1)) FD(1) FIN ACK(FIN) (close) (close) Figure 2-12: Time-out Triggered NAK Retransmission Sender Receiver Sender Receiver M M FD(1) FD(1) FD(2) FD(2) FD (last) FD(last) timeout EOF X EOF ACK(EOF) EOF FIN ACK(EOF) X timeout FIN FIN ACK(FIN) (close) (close) ACK(FIN) (close) (close) (a) (b) Figure 2-13: Time-out Triggered EOF and Finished Retransmissions CCSDS 720.1-G-3 Page 2-23 April 2007
CCSDS REPORT CONCERNING THE CCSDS FILE DELIVERY PROTOCOL (CFDP) In addition to the time-outs just described, there is an overall inactivity timer. If there is a cessation of PDU reception for a given Transaction for the specified time period, this timer causes the issuance of a Fault indication, with a condition code identifying the condition ‘Inactivity’ to the local user. It takes no other action. That is, any further resulting action is not specified by the protocol, but is taken by the user in an implementation-specific manner. The user might try to restart or otherwise salvage the Transaction, abandon it, or take some other action appropriate to the implementation and operational configuration. The basic purpose of the timer is to handle situations that are outside the protocol itself. Examples might be the crashing of the operating system in the other entity party to the ongoing Transaction, the extended failure of an intermediate communication link, etc. This timer is mandatory, except that it is not used at the Source end of an unacknowledged mode transfer. 2.7 PRIMITIVES, PDUS, AND PIPES The ‘spawning’ relationships between Request Primitives and PDUs, and between PDUs and Indication Primitives in the operational process from initiation through termination, is shown in figure 2-14. Figure 2-15 is a ‘pipe’ diagram of the CFDP showing several of the possible lower layers. The examples of lower layers shown in the figure are just that, examples, and are not intended to be all-inclusive. Figure 2-16 shows a possible example implementation involving a spacecraft, a ground station and a control center. (Refer also to 3.2.1.3 and 3.2.1.4.) CCSDS 720.1-G-3 Page 2-24 April 2007
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CCSDS File Delivery Protocol (CFDP)âPart 1: Introduction and ...

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CCSDS File Delivery Protocol (CFDP)âPart 1: Introduction and ...